1. Field of Invention
The present invention relates to the field of control systems. In particular, the present invention describes a control system having improved reliability and extendibility for semiconductor processing equipment.
2. Description of Related Art
Semiconductor manufacturers use semiconductor wafers as the base for manufacturing integrated circuits. In one step of the manufacturing process, the wafers are put through a chemical-mechanical polishing step that leaves the wafers' surfaces covered in particles. Semiconductor manufacturers use double sided wafer scrubbers (scrubbers) to clean the semiconductor wafers after being polished. Double sided wafer scrubbers clean both sides of each wafer to remove these particles.
To reduce the risk of damaging the wafers, automated scrubbers have been developed. Scrubbers typically include a number of automated stations that operate together to clean wafers. Typically, to clean a wafer, the wafer must first be loaded from the cassette (a device for holding wafers), washed, brushed, dried, and then placed into another cassette. Typically, a scrubber cleans multiple wafers at the same time; one wafer being in each station.
Scrubber customers demand scrubbers that can continuously repeat the processing steps for many wafers with very few differences between the processing of individual wafers. This repeatability of the wafer processing is important to scrubber customers.
To reduce the costs of supporting scrubber customers, the reliability of the scrubbers must be very high. Typically, semiconductor equipment manufacturers sell their products globally. Therefore, correcting problems on a scrubber can be expensive as technicians may need to travel great distances at significant cost.
Scrubber customers often require special modifications to a basic scrubber design. For example, a customer may require that the scrubber's output station provide wafers to another semiconductor processing station. These special modifications can be expensive to implement.
One prior art scrubber, the DDS-200 Doubled Sided Scrubber, available from OnTrak Systems, Inc., of Milpitas, Calif., achieved many of these goals. However, customers continue to demand scrubbers with greater repeatability, higher reliability, and more features. To meet these customer demands, an improved control system is needed.